Microcapsules

ABSTRACT

The present invention concerns microcapsules comprising a capsule core and a capsule wall, the capsule wall being constructed from
     30% to 90% by weight of one or more C 1 -C 24 -alkyl esters of acrylic and/or methacrylic acid, acrylic acid, methacrylic acid and/or maleic acid (monomers I),   10% to 70% by weight of a mixture of divinyl and polyvinyl monomers (monomers II), the fraction of polyvinyl monomers being in the range from 2% to 90% by weight based on the monomers II, and also   0% to 30% by weight of one or more miscellaneous monomers (monomer III),
 
all based on the total weight of the monomers, a process for their production and their use in textiles, bindered building materials and heat transfer fluids.

The present invention concerns microcapsules comprising a capsule coreand a capsule wall constructed of C₁-C₂₄-alkyl esters of acrylic and/ormethacrylic acid, acrylic acid, methacrylic acid and/or maleic acid,crosslinkers and also, if appropriate, miscellaneous monomers. Thepresent invention also concerns a process for their production and theiruse in textiles, bindered building materials and heat transfer fluids.

Textiles combined with latent heat storage media have been studied as anovel combination of materials in recent years. The working principle oflatent heat storage media, often also known as phase change materials(PCMs), relies on the transformation enthalpy which arises during thesolid/liquid phase transition and which signifies an absorption ofenergy or release of energy to the environment. They can consequently beused to keep a temperature constant within a fixed temperature range.

EP-A 1 029 018 teaches the use of microcapsules having a capsule wall ofa highly crosslinked methacrylic ester polymer and a latent heat storagecore in bindered building materials such as concrete or gypsum. DE-A 10139 171 describes the use of microencapsulated latent heat storagematerials in gypsum plasterboards. Furthermore, WO 2005/116559 teachesthe use of microencapsulated latent heat storage materials in chipboardpanels together with melamine-formaldehyde resins as a binder.

EP-A 1 321 182 teaches microencapsulated latent heat storage materialshaving a capsule wall of a highly crosslinked methacrylic ester polymerand also nominates their use in textiles. This reference teachesmicrocapsular dispersions having a particularly low fraction of capsules≦4 μm in particle size.

EP-A 1 251 954 and WO 2005/105291 teach microcapsules based onpolymethacrylic acid with or without butanediol diacrylate as acrosslinker. The capsules having particle sizes of 1.2 μm are used forimpregnating fibers.

An important criterion for applications as a finish in the textilesector is durability to dry cleaning, i.e., resistance to chlorinated orperchlorinated solvents. There is often a weight loss in the case ofconventional microcapsules, indicative of insufficiently tight ordefective capsules. Such washout losses can be in the range of 5-15% byweight.

The two prior European applications No. 06117092.4 and No. 06122419.2propose microcapsules whose surface has been additionally modified witha polyelectrolyte as a way to solve the problem.

As well as a lower washout loss, a low evaporation rate is an importantrequirement for the capsules, since the capsules are generally processedat high temperatures. While textile applications require anevaporation-rate performance able to cope with challenges posed bycomparatively brief thermal loads, good tightness over a long period isrequired for applications in the building sector.

It is an object of the present invention to provide microcapsules havinga low evaporation rate for a wide variety of capsule size distributions.

We have found that this object is achieved by microcapsules comprising acapsule core and a capsule wall, the capsule wall being constructed from

-   30% to 90% by weight of one or more C₁-C₂₄-alkyl esters of acrylic    and/or methacrylic acid, acrylic acid, methacrylic acid and/or    maleic acid (monomers I),-   10% to 70% by weight of a mixture of divinyl and polyvinyl monomers    (monomers II), the fraction of polyvinyl monomers being in the range    from 2% to 90% by weight based on the monomers II, and also-   0% to 30% by weight of one or more miscellaneous monomers (monomer    III),    all based on the total weight of the monomers, a process for their    production and their use in textiles, bindered building materials    and heat transfer fluids.

The microcapsules of the present invention comprise a capsule core and acapsule wall. The capsule core consists predominantly, to more than 95%by weight, of lipophilic substance. The average particle size of thecapsules (Z-average by light scattering) is in the range from 0.5 to 100μm, preferably in the range from 1 to 80 μm and particularly in therange from 1 to 50 μm.

In one preferred embodiment, the average particle size of the capsulesis in the range from 1.5 to 2.5 μm and preferably in the range from 1.7to 2.4 μm. And 90% of the particles have a particle size (diameter) ≦4μm, preferably ≦3.5 μm and particularly ≦3 μm. The full width at halfmaximum value of the microcapsular dispersion is preferably in the rangefrom 0.2 to 1.5 μm and particularly in the range from 0.4 to 1 μm.

In a likewise preferred embodiment, the average particle size of thecapsules is >2.5 to 20 μm and preferably in the range from 3.0 to 15 μm.

The weight ratio of capsule core to capsule wall is generally in therange from 50:50 to 95:5. A core/wall ratio in the range from 70:30 to93:7 is preferred.

The polymers of the capsule wall comprise generally at least 30% byweight, preferably at least 35% by weight and more preferably at least40% by weight and also generally not more than 90% by weight, preferablynot more than 80% by weight and more preferably not more than 75% byweight of C₁-C₂₄-alkyl esters of acrylic and/or methacrylic acid,acrylic acid, methacrylic acid and/or maleic acid (monomers I) ininterpolymerized form, based on the total weight of the monomers.

According to the present invention, the polymers of the capsule wallcomprise in general at least 10% by weight, preferably at least 15% byweight and more preferably at least 20% by weight and in general notmore than 70% by weight, preferably not more than 60% by weight and morepreferably not more than 50% by weight of a mixture of divinyl andpolyvinyl monomers (together monomers II) in interpolymerized form,based on the total weight of the monomers. One or more divinyl monomersand also one or more polyvinyl monomers may be interpolymerized.

Monomers II comprises a mixture of divinyl and polyvinyl monomerswherein the fraction of polyvinyl monomers is in the range from 2% to90% by weight, based on the sum total of divinyl and polyvinyl monomers.The fraction of polyvinyl monomers is preferably in the range from 5% to80% by weight and more preferably in the range from 10% to 60% byweight, based on the sum total of divinyl and polyvinyl monomers. Formicrocapsules having an average particle size <2.5 μm, the polyvinylmonomer fraction is preferably in the range from 20% to 80% by weightand particularly in the range from 30% to 60% by weight based on the sumtotal of divinyl and polyvinyl monomers. For microcapsules having anaverage particle size ≧2.5 μm, the polyvinyl monomer fraction ispreferably in the range from 5% to 40% by weight and particularly in therange from 10% to 30% by weight based on the sum total of divinyl andpolyvinyl monomers.

In addition, the polymers may comprise up to 30% by weight, preferablyup to 20% by weight, particularly up to 10% by weight and morepreferably up to 5% by weight and also at least 1% by weight ofmiscellaneous monomers III, preferably monomers IIIa, ininterpolymerized form, based on the total weight of the monomers.

Preferably, the capsule wall is only constructed from monomers of groupsI and II.

Suitable monomers I include C₁-C₂₄-alkyl esters of acrylic and/ormethacrylic acid (monomers Ia). They further include the unsaturated C₃-and C₄-carboxylic acids such as acrylic acid, methacrylic acid and alsomaleic acid (monomers Ib). Particularly preferred monomers I are methylacrylate, ethyl acrylate, n-propyl acrylate and n-butyl acrylate and/orthe corresponding methacrylates. Preference is given to isopropylacrylate, isobutyl acrylate, sec-butyl acrylate and tert-butyl acrylateand the corresponding methacrylates. In general, the methacrylates andmethacrylic acid are preferred.

In one preferred embodiment, the microcapsule walls are constructed from25% by weight to 75% by weight of maleic acid and/or acrylic acidparticularly methacrylic acid.

Suitable divinyl monomers include divinylbenzene, trivinylbenzene anddivinylcyclo-hexane and trivinylcyclohexane. Preferred divinyl monomersare the diesters of diols with acrylic acid or methacrylic acid and alsothe diallyl and divinyl ethers of these diols. Ethanediol diacrylate,ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate,methallylmethacrylamide, allyl acrylate and allyl methacrylate may bementioned by way of example. Particular preference is given topropanediol diacrylate, butanediol diacrylate, pentanediol diacrylateand hexanediol diacrylate and the corresponding methacrylates.

Preferred polyvinyl monomers are the polyesters of polyols with acrylicacid and/or methacrylic acid and also the polyallyl and polyvinyl ethersof these polyols. Preference is given to trimethylolpropane triacrylate,trimethylolpropane trimethacrylate, pentaerythritol triallyl ether,pentaerythritol tetraallyl ether, pentaerythritol triacrylate andpentaerythritol tetraacrylate and also their technical grade mixtures.

Preference is given to the combinations of butanediol diacrylate andpentaerythritol tetraacrylate, hexanediol diacrylate and pentaerythritoltetraacrylate, butanediol diacrylate and trimethylolpropane triacrylate,and also hexanediol diacrylate and trimethylolpropane triacrylate.

Monomers III are miscellaneous monomers other than monomers I and II,such as vinyl acetate, vinyl propionate, vinylpyridine and styrene orα-methylstyrene. Particular preference is given to monomers IIIa whichbear charge-carrying or ionizable groups and differ from the monomers Iand II, such as itaconic acid, maleic anhydride, 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate,acrylamido-2-methylpropane-sulfonic acid, methacrylonitrile,acrylonitrile, methacrylamide, N-vinylpyrrolidone, N-methylolacrylamide,N-methylolmethacrylamide, dimethylaminoethyl methacrylate anddiethylaminoethyl methacrylate.

The capsule wall is preferably constructed from

-   30% to 90% by weight of a mixture of monomers Ia and Ib wherein the    fraction of monomers Ib is <25% by weight based on the total weight    of all monomers I, II and III,-   10% to 70% by weight of a mixture of divinyl and polyvinyl monomers    (monomers II) wherein the fraction of polyvinyl monomers is 2% to    90% by weight based on the monomers II, and also-   0% to 30% by weight of miscellaneous monomers III,    all based on the total weight of the monomers.

In a further preferred embodiment, the capsule wall is constructed from

-   30% to 90% by weight of a mixture of monomers Ia and Ib wherein the    fraction of monomers Ib is ≧25% by weight based on the total weight    of all monomers I, II and III,-   10% to 70% by weight of a mixture of divinyl and polyvinyl monomers    (monomers II) wherein the fraction of polyvinyl monomers is 2% to    90% by weight based on the monomers II, and also-   0% to 30% by weight of miscellaneous monomers III,    all based on the total weight of the monomers.

The microcapsules of the present invention are obtainable via aso-called in situ polymerization. The principle of microcapsuleformation is based on a stable oil-in-water emulsion being prepared fromthe monomers, a free-radical initiator, a protective colloid and thelipophilic substance to be encapsulated. Polymerization of the monomersis then triggered by heating and if appropriate controlled through afurther temperature increase, the resulting polymers forming the capsulewall which surrounds the lipophilic substance. This general principle isdescribed for example in DE-A-10 139 171, the content of which is herebyexpressly incorporated by reference.

In general, the microcapsules are produced in the presence of at leastone organic or inorganic protective colloid. Organic and inorganicprotective colloids may be ionic or neutral. Protective colloids can beused not only individually but also in mixtures of a plurality ofidentically or differently charged protective colloids.

Organic protective colloids are preferably water-soluble polymers whichreduce the surface tension of water from a maximum of 73 mN/m to therange from 45 to 70 mN/m and thus ensure the formation of uninterruptedcapsule walls and also form micro-capsules having preferred particlesizes in the range from 0.5 to 50 μm, preferably in the range from 0.5to 30 μm and particularly in the range from 0.5 to 10 m.

Organic neutral protective colloids include for example cellulosederivatives such as hydroxyethylcellulose, methylhydroxyethylcellulose,methylcellulose and carboxy-methylcellulose, polyvinylpyrrolidone,copolymers of vinylpyrrolidone, gelatin, gum arabic, xanthan, casein,polyethylene glycols, polyvinyl alcohol and partially hydrolyzedpolyvinyl acetates and also methylhydroxypropylcellulose. Preferredorganic neutral protective colloids are polyvinyl alcohol and partiallyhydrolyzed polyvinyl acetates and also methylhydroxypropylcellulose.

Organic anionic protective colloids include sodium alginate,polymethacrylic acid and its copolymers, the copolymers of sulfoethylacrylate, of sulfoethyl methacrylate, of sulfopropyl acrylate, ofsulfopropyl methacrylate, of N-(sulfoethyl)-maleimide, of2-acrylamido-2-alkylsulfonic acids, styrenesulfonic acid and also ofvinylsulfonic acid. Preferred organically anionic protective colloidsare naphthalenesulfonic acid and naphthalenesulfonic acid-formaldehydecondensates and, in particular, polyacrylic acids and phenolsulfonicacid-formaldehyde condensates.

Pickering systems are an example of useful inorganic protectivecolloids. Pickering systems facilitate stabilization through very finesolid particles and are insoluble but dispersible in water or areinsoluble and nondispersible in water but wettable by the lipophilicsubstance. Their mode of action and their use is described in EP-A-1 029018 and also EP-A-1 321 182, both expressly incorporated herein byreference.

A Pickering system in this context can consist of the solid particles ontheir own or additionally of auxiliary materials which improve thedispersibility of the particles in water or the wettability of theparticles by the lipophilic phase.

The inorganic solid particles may be metal salts, such as salts, oxidesand hydroxides of calcium, magnesium, iron, zinc, nickel, titanium,aluminum, silicon, barium and manganese. Examples are magnesiumhydroxide, magnesium carbonate, magnesium oxide, calcium oxalate,calcium carbonate, barium carbonate, barium sulfate, titanium dioxide,aluminum oxide, aluminum hydroxide and zinc sulfide. Silicates,bentonite, hydroxyapatite and hydrotalcites may likewise be mentioned.Particular preference is given to finely divided silicas, magnesiumpyrophosphate and tricalcium phosphate.

The Pickering systems may be introduced, firstly, into the water phase,or be added to the stirred emulsion of oil-in-water. Some fine, solidparticles are obtained by a precipitation as described in EP-A 1 029 018and also EP-A 1 321 182.

Finely divided silicas may be dispersed in water as fine, solidparticles. However, it is also possible to use so-called colloidaldispersions of silica in water. Such colloidal dispersions are alkaline,aqueous mixtures of silica. In the alkaline pH range, the particles areswollen and stable in water. For these dispersions to be used as aPickering system, it is advantageous when the pH of the oil-in-wateremulsion is adjusted to pH 2-7 with an acid.

Preference is given to using organic protective colloids if appropriatein admixture with inorganic protective colloids.

In general, the protective colloids are used in amounts of 0.1% to 15%by weight and preferably 0.5% to 10% by weight, based on the waterphase. The amounts for inorganic protective colloids preferably rangefrom 0.5% to 15% by weight, based on the water phase. Organic protectivecolloids are preferably used in amounts of 0.1% to 10% by weight, basedon the water phase of the emulsion.

One embodiment has a preference for inorganic protective colloids andtheir mixtures with organic protective colloids.

A further embodiment has a preference for organically neutral protectivecolloids. Particular preference is given to OH-bearing protectivecolloids such as polyvinyl alcohols and partially hydrolyzed polyvinylacetates.

In general, polyvinyl alcohol and/or partially hydrolyzed polyvinylacetate are used in a total amount of at least 3% by weight andpreferably in the range from 6% to 8% by weight, based on themicrocapsules (without protective colloid). It is possible to addfurther abovementioned protective colloids additionally to the preferredamounts of polyvinyl alcohol or partially hydrolyzed polyvinyl acetate.Preferably, the microcapsules are only produced using polyvinyl alcoholand/or partially hydrolyzed polyvinyl acetate and without inclusion offurther protective colloids.

A further embodiment has a preference for mixtures of organic protectivecolloids such as polyvinyl alcohols together with cellulose derivatives.

Polyvinyl alcohol is obtainable by polymerizing vinyl acetate, ifappropriate in the presence of comonomers, and hydrolyzing the polyvinylacetate to detach the acetyl groups to form hydroxyl groups. The degreeof hydrolysis of the polymers can be for example in the range from 1% to100% and is preferably in the range from 50% to 100% and particularly inthe range from 65% to 95%. Partially hydrolyzed polyvinyl acetatesherein have a degree of hydrolysis of <50%, while polyvinyl alcoholherein has a degree of hydrolysis of ≧50% to 100%. The synthesis ofhomo- and copolymers of vinyl acetate and the hydrolysis of thesepolymers to form polymers comprising vinyl alcohol units is commongeneral knowledge. Polymers comprising vinyl alcohol units are marketedfor example as Mowiol® brands by Kuraray Specialities Europe (KSE).

Preference is given to polyvinyl alcohols and/or partially hydrolyzedpolyvinyl acetates whose DIN 53015 viscosity at 20° C. in 4% by weightaqueous solution is in the range from 3 to 56 mPa·s and preferably inthe range from 14 to 45 mPa·s. Preference is given to polyvinyl alcoholshaving a degree of hydrolysis of ≧65%, preferably ≧70% and particularly≧75%.

The use of polyvinyl alcohol and/or partially hydrolyzed polyvinylacetate leads to stable emulsions even for small average particle sizessuch as 1.5-2.5 μm. The size of the oil droplets is substantially equalto the size of the as-polymerized microcapsules.

The process for producing microcapsules by

-   -   a) producing an oil-in-water emulsion comprising the monomers,        the lipophilic substance and polyvinyl alcohol and/or partially        hydrolyzed polyvinyl acetate, the average size of the oil        droplets being 1.5-2.5 μm, and    -   b) free-radically polymerizing the monomers of the oil-in-water        emulsion obtained by a).

Useful free-radical initiators for the free-radical polymerizationreaction include the customary peroxo and azo compounds, advantageouslyin amounts of 0.2% to 5% by weight, based on the weight of the monomers.

Depending on the physical state of the free-radical initiator and itssolubility characteristics, the free-radical initiator can be added assuch, but is preferably added as a solution, emulsion or suspensionbecause small quantities in particular of free-radical initiator aremetered more precisely.

Preferred free-radical initiators are tert-butyl peroxyneodecanoate,tert-amyl peroxypivalate, dilauroyl peroxide, tert-amylperoxy-2-ethylhexanoate, 2,2′-azobis-(2,4-dimethyl)valeronitrile,2,2′-azobis(2-methylbutyronitrile), dibenzoyl peroxide, tert-butylper-2-ethylhexanoate, di-tert-butyl peroxide, tert-butyl hydroperoxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and cumene hydroperoxide.

Particularly preferred free-radical initiators aredi(3,5,5-trimethylhexanoyl) peroxide, 4,4′-azobisisobutyronitrile,tert-butyl perpivalate and dimethyl 2,2-azobisisobutyrate. These have ahalf-life of 10 hours in a temperature range from 30 to 100° C.

It is further possible to add customary amounts of conventionalregulators such as tert-dodecyl mercaptan or ethylhexyl thioglycolate tothe polymerization.

The temperature at which the polymerization is carried out is generallyin the range from 20 to 100° C. and preferably in the range from 40 to95° C. Depending on the desired lipophilic substance, the oil-in-wateremulsion is to be formed at a temperature at which the core material isliquid/oily. Accordingly, the free-radical initiator chosen has to haveits disintegration temperature above this temperature and thepolymerization likewise has to be carried out at from 2 to 50° C. abovethis temperature, so that free-radical initiators whose disintegrationtemperature is above the melting point of the lipophilic substance arechosen, if appropriate.

A common process variant for lipophilic substances having a meltingpoint of up to about 60° C. is a reaction temperature starting at 60°C., which is raised to 85° C. in the course of the reaction.Advantageous free-radical initiators have a 10 hour half-life in therange from 45 to 65° C. such as t-butyl perpivalate.

In a further process variant for lipophilic substances having a meltingpoint above 60° C., a temperature program which starts atcorrespondingly higher reaction temperatures is chosen. Free-radicalinitiators having a 10 hour half-life in the range from 70 to 90° C. arepreferred for initial temperatures of around 85° C. such as t-butylper-2-ethyl-hexanoate.

The polymerization is conveniently carried out at atmospheric pressure,but can also be carried out at reduced or slightly elevated pressure,for example at a polymerization temperature above 100° C., i.e., in therange from 0.5 to 5 bar, say.

The reaction times for the polymerization are normally in the range from1 to 10 hours and usually in the range from 2 to 5 hours.

A present invention process variant utilizing polyvinyl alcohol and/orpartially hydrolyzed polyvinyl acetate makes for an advantageous processmethod whereby dispersion and polymerization are carried out directly atelevated temperature.

After the actual polymerization reaction at a conversion of 90% to 99%by weight, it is generally advantageous to render the aqueousmicrocapsular dispersions largely free of odor carriers, such asresidual monomers and other organic volatile constituents. This can beachieved in a manner known per se by physical means by distillativeremoval (in particular by means of steam distillation) or by strippingwith an inert gas. It may also be carried out by chemical means, asdescribed in WO 99/24525, advantageously by redox-initiatedpolymerization, as described in DE-A 44 35 423, DE-A 44 19 518 and DE-A44 35 422.

The microcapsules of the present invention are useful, depending on thelipophilic substance, for carbonless copypaper, in cosmetics, forencapsulating adhesives, adhesives components, catalysts or in cropprotection or generally for encapsulating biocides. The microcapsules ofthe present invention are particularly useful for latent heat storagematerials.

Latent heat storage materials are by definition substances having aphase transition in the temperature range in which heat transfer is totake place. Preferably, the lipophilic substance has a solid/liquidphase transition in the temperature range from −20 to 120° C.

Examples of suitable substances are:

-   -   aliphatic hydrocarbyl compounds such as saturated or unsaturated        C₁₀-C₄₀-hydrocarbons, which are branched or preferably linear,        e.g. such as n-tetra-decane, n-pentadecane, n-hexadecane,        n-heptadecane, n-octadecane, n-nonadecane, n-eicosane,        n-heneicosane, n-docosane, n-tricosane, n-tetracosane,        n-pentacosane, n-hexacosane, n-heptacosane, n-octacosane and        cyclic hydrocarbons, e.g. cyclohexane, cyclooctane, cyclodecane;    -   aromatic hydrocarbyl compounds, such as benzene, naphthalene,        biphenyl, o- or n-terphenyl, C₁-C₄₀-alkyl-substituted aromatic        hydrocarbons, such as dodecylbenzene, tetradecylbenzene,        hexadecylbenzene, hexylnaphthalene or decylnaphthalene;    -   saturated or unsaturated C₆-C₃₀-fatty acids, such as lauric,        stearic, oleic or behenic acid, preferably eutectic mixtures of        decanoic acid with e.g. myristic, palmitic or lauric acid;    -   fatty alcohols, such as lauryl, stearyl, oleyl, myristyl, cetyl        alcohol, mixtures such as coconut fatty alcohol, and the        so-called oxo alcohols which are obtained by hydroformylation of        α-olefins and further reactions;    -   C₆-C₃₀-fatty amines, such as decylamine, dodecylamine,        tetradecylamine or hexadecylamine;    -   esters such as C₁-C₁₀-alkyl esters of fatty acids, such as        propyl palmitate, methyl stearate or methyl palmitate, and        preferably their eutectic mixtures or methyl cinnamate;    -   natural and synthetic waxes, such as montan acid waxes, montan        ester waxes, carnauba wax, polyethylene wax, oxidized waxes,        polyvinyl ether wax, ethylene vinyl acetate wax or hard waxes in        accordance with Fischer-Tropsch processes;    -   halogenated hydrocarbons, such as chloroparaffin,        bromooctadecane, bromopentadecane, bromononadecane,        bromoeicosane, bromodocosane.

Mixtures of these substances are also suitable provided the meltingpoint is not lowered outside of the desired range, or the heat of fusionof the mixture is too low for sensible application.

For example, the use of pure n-alkanes, n-alkanes with a purity greaterthan 80% or of alkane mixtures as are produced as technical-gradedistillate and as such are commercially available is advantageous.

In addition, it may be advantageous to add to the lipophilic substancescompounds which are soluble therein in order to prevent the delayedcrystallization which sometimes arises with nonpolar substances. Asdescribed in U.S. Pat. No. 5,456,852 it is advantageous to use compoundswith a melting point at from 20 to 120 K higher than the actual coresubstance. Suitable compounds are the fatty acids, fatty alcohols, fattyamides and aliphatic hydrocarbyl compounds mentioned above as lipophilicsubstances. They are added in amounts of from 0.1% to 10% by weight,based on the capsule core.

The latent heat storage materials are chosen according to thetemperature range in which the heat storage media are desired. Forexample, for heat storage media in building materials in a moderateclimate, preference is given to using latent heat storage materialswhose solid/liquid phase transition is in the temperature range from 0to 60° C. Thus, for interior applications, individual materials ormixtures with conversion temperatures of from 15 to 30° C. are usuallychosen. In the case of solar applications as storage medium or foravoiding the overheating of transparent thermal insulation, as describedin EP-A 333 145, conversion temperatures of 30-60° C. are especiallysuitable. Conversion temperatures of 0 to 40° C. are advantageous forapplications in the textile sector in particular and of −10 to 120° C.for heat transfer fluids in particular.

Preferred latent heat storage materials are aliphatic hydrocarbons,particularly preferably those listed above by way of example. Particularpreference is given to aliphatic hydrocarbons having 14 to 20 carbonatoms, and mixtures thereof.

In one preferred embodiment, polyelectrolytes are additionally disposedon the outer surface of the capsule wall. Depending on the amount ofpolyelectrolyte, the polyelectrolyte arrangement on the surface takesthe form of points, spots or dots, or takes the form of regions whichcan extend to where the polyelectrolyte forms a uniform arrangementwhich resembles a layer, sheath, shell or envelope.

In general, the fraction of polyelectrolytes is in the range from 0.1%to 10% by weight based on the total weight of thepolyelectrolyte-bearing microcapsules. Preferably the polyelectrolytefraction is 0.5%-5% by weight and in particular 1%-3% by weight based onthe total weight of the polyelectrolyte-bearing microcapsules.

Different wall thicknesses can be necessary depending on the field ofuse, so that it can further be sensible to orient the amount ofpolyelectrolyte on the basis of the total amount of monomers in thewall.

The preferred amount of polyelectrolyte in one embodiment is accordinglyin the range from 10% to 30% by weight based on the total amount of themonomers in the wall material.

In another embodiment, the preferred amount of polyelectrolyte is in therange from 5% to 15% by weight based on the total amount of the monomersin the wall material.

The term polyelectrolyte generally refers to polymers having ionizableor ionically dissociable groups which can be a polymer chain constituentor substituent. Typically, the number of these ionizable or ionicallydissociable groups in the polyelectrolyte is so large that the polymersare water soluble or swellable in the ionic form (also known aspolyions). Preference is given to polyelectrolytes which have asolubility of ≧4 g/l in water at 25° C., in particular polyelectrolyteshaving unlimited solubility in water. Preference is given topolyelectrolytes that bear an electrolyte functionality on each repeatunit.

Unlike protective colloids, polyelectrolytes generally have little ifany emulsifying effect and have predominantly a thickening effect. Inthe realm of the present invention, polyelectrolytes have an averagemolecular weight in the range from 500 to 10 000 000 g/mol, preferablyin the range from 1000 to 100 000 g/mol and in particular in the rangefrom 1000 to 10 000 g/mol. Linear or branched polyelectrolytes can beused. Unlike the protective colloids used in the realm of the presentinvention, which are added before the polymerization, to form theoil-in-water emulsion, polyelectrolytes in the realm of the presentinvention are polymers having ionizable or ionically dissociable groupswhich are brought into contact with the microcapsules—afterpolymerization has taken place, that is—in an aqueous medium, preferablywater. Aqueous medium refers to aqueous mixtures comprising up to 10% byweight based on the aqueous medium of a water-miscible solvent which ismiscible with water at 25° C. and 1 bar in the desired amount. Thesesolvents include alcohols such as methanol, ethanol, propanol,isopropanol, glycol, glycerol and methoxyethanol and water-solubleethers such as tetrahydrofuran and dioxane and also aprotic additivessuch as dimethylformamide or dimethyl sulfoxide.

Depending on the identity of the dissociable groups, there are cationicand anionic polyelectrolytes (also known as polyions). The charge on thepolyion is considered, without counter-ion. Cationic polyelectrolytesare formed from polymers comprising basic groups (polybases) by additionof protons or quaternization.

Anionic polyelectrolytes are formed from polymers comprising acidicgroups (polyacids) by detachment of protons.

The polyelectrolyte is classified according to the resulting net chargeof the polyion (i.e., without counter-ion). When the polyelectrolyte haspredominantly positively charged, dissociated groups, it is a cationicpolyelectrolyte. When it has predominantly negatively charged groups, itis an anionic polyelectrolyte.

Preference is given to using one or more cationic or one or more anionicpolyelectrolytes. Particular preference is given to choosing one or morecationic polyelectrolytes. It is believed that successive addition of aplurality of differently charged polyelectrolytes will lead to theconstruction of a plurality of layers, provided the amount ofpolyelectrolyte is in each case sufficient to construct a layer. Ingeneral, an amount of at least 1% by weight of polyelectrolyte based onthe total weight of the polyelectrolyte-bearing microcapsules will leadto coating with a layer. Preferably, however, only one layer ofpolyelectrolyte is applied. This layer may comprise one polyelectrolyteor a mixture of a plurality of polyelectrolytes having the same charge.

Anionic polyelectrolytes are obtainable for example by free-radicalpolymerization of ethylenically unsaturated anionic monomers in anaqueous medium. Useful ethylenically unsaturated anionic monomersinclude for example monoethylenically unsaturated C₃- to C₅-carboxylicacids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonicacid, maleic acid, fumaric acid and itaconic acid, sulfonic acids suchas vinylsulfonic acid, styrenesulfonic acid andacrylamidomethylpropanesulfonic acid and phosphonic acids such asvinylphosphonic acid, and/or the respective alkali metal, alkaline earthmetal and/or ammonium salts thereof.

Preferred anionic monomers include acrylic acid, methacrylic acid,maleic acid and acrylamido-2-methylpropanesulfonic acid. Particularpreference is given to aqueous dispersions of polymers based on acrylicacid. The anionic monomers can be polymerized either alone, to formhomopolymers, or else in admixture with each other, to form copolymers.Examples thereof are the homopolymers of acrylic acid, homopolymers ofmethacrylic acid or copolymers of acrylic acid and maleic acid,copolymers of acrylic acid and methacrylic acid and also copolymers ofmethacrylic acid and maleic acid.

However, anionic monomers can also be polymerized in the presence of atleast one other ethylenically unsaturated monomer. These monomers can benonionic or alternatively bear a cationic charge.

Examples of nonionic comonomers are acrylamide, methacrylamide, N—C₁- toC₃-alkyl-acrylamides, N-vinylformamide, acrylic esters of monohydricalcohols having 1 to 20 carbon atoms such as in particular methylacrylate, ethyl acrylate, isobutyl acrylate and n-butyl acrylate,methacrylic esters of monohydric alcohols having 1 to 20 carbon atomsfor example methyl methacrylate and ethyl methacrylate, and also vinylacetate and vinyl propionate.

Useful cationic monomers for copolymerization with anionic monomersinclude dialkyl-aminoethyl acrylates, dialkylaminoethyl methacrylates,dialkylaminopropyl acrylates, dialkylaminopropyl methacrylates,dialkylaminoethylacrylamides, dialkylaminoethyl-methacrylamides,dialkylaminopropylacrylamides, dialkylaminopropylmethacrylamides,diallyldimethylammonium chloride, vinylimidazole, and also cationicmonomers each neutralized and/or quaternized with mineral acids.Specific examples of cationic monomers are dimethylaminoethyl acrylate,dimethylaminoethyl methacrylate, diethylaminoethyl acrylate,diethylaminoethyl methacrylate, dimethylaminopropyl acrylate,dimethylaminopropyl methacrylate, diethylaminopropyl acrylate anddiethylaminopropyl methacrylate, dimethylaminoethylacrylamide,dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide,dimethylaminopropylmethacrylamide, diethylaminoethylacrylamide anddiethylaminopropylacrylamide.

Cationic monomers can be completely or else only partially neutralizedor quaternized, for example to an extent in each case from 1% to 99%.Dimethyl sulfate is the preferred quaternizing agent for cationicmonomers. However, the monomers can also be quaternized with diethylsulfate or with alkylating agents, in particular alkyl halides such asmethyl chloride, ethyl chloride or benzyl chloride. Comonomers forpreparing anionic polyelectrolytes are used for example in such amountsthat the resulting dispersions of polymer, on diluting with water and atabove pH 7.0 and at 20° C., are water soluble and have an anioniccharge. Based on total monomers used in the polymerization, the amountof nonionic and/or cationic comonomers is for example in the range from0% to 99% by weight and preferably in the range from 5% to 75% by weightand is usually in the range from 5% to 25% by weight. Cationic monomersare used at most in an amount such that the resulting polyelectrolyteshave a net anionic charge at pH<6.0 and 20° C. The excess anionic chargein the amphoteric polymers formed is for example at least 5 mol %,preferably at least 10 mol %, in particular at least 30 mol % and mostpreferably at least 50 mol %.

Examples of preferred copolymers are copolymers composed of 25% to 90%by weight acrylic acid and 75% to 10% by weight acrylamide. Preferably,at least one ethylenically unsaturated C₃ to C₅-carboxylic acid ispolymerized in the absence of other monoethylenically unsaturatedmonomers. Particular preference is given to homopolymers of acrylic acidwhich are obtainable by free-radical polymerization of acrylic acid inthe absence of other monomers.

Useful crosslinkers for preparing branched polyelectrolytes include allcompounds having at least two ethylenically unsaturated double bonds inthe molecule. Such compounds are used for example in the preparation ofcrosslinked polyacrylic acids such as superabsorbent polymers, cf. EP-A0 858 478 page 4 line 30 to page 5 line 43. Examples of crosslinkers aretriallylamine, pentaerythritol triallyl ether, pentaerythritoltetraallyl ether, methylenebisacrylamide, N,N′-divinylethyleneurea, atleast diallyl ethers or at least divinyl ethers of polyhydric alcoholssuch as for example sorbitol, 1,2-ethanediol, 1,4-butanediol,trimethylolpropane, glycerol, diethylene glycol, and of sugars such assucrose, glucose, mannose, fully acrylated or methacrylated dihydricalcohols having 2 to 4 carbon atoms such as ethylene glycoldimethacrylate, ethylene glycol diacrylate, butanediol dimethacrylate,butanediol diacrylate, diacrylates or dimethacrylates of polyethyleneglycols having molecular weights from 300 to 600, ethoxylatedtrimethylenepropane triacrylates or ethoxylated trimethylenepropanetrimethacrylates, 2,2-bis(hydroxymethyl)butanol trimethacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate andtriallylmethylammonium chloride. When crosslinkers are used in thepreparation of the dispersions of the present invention, the amounts ofcrosslinker which are used in each case are for example from 0.0005% to5.0% by weight and preferably from 0.001% to 1.0% by weight, based ontotal monomers used in the polymerization. Preferred crosslinkers arepentaerythritol triallyl ether, pentaerythritol tetraallyl ether,N,N′-divinylethyleneurea, at least diallyl ethers of sugars such assucrose, glucose or mannose and triallylamine, and also mixturesthereof.

Useful anionic polyelectrolytes further include polycondensates such asfor example phenolsulfonic acid resins. Of suitability are aldehydecondensates, particularly on the basis of formaldehyde, acetaldehyde,isobutyraldehyde, propionaldehyde, glutaraldehyde and glyoxal, and veryparticularly formaldehyde condensates based on phenolsulfonic acids.Amines and amides, in particular those of carbonic acid such as forexample urea, melamine or dicyandiamide are examples of further reactingcompounds which can be co-used for preparing the phenolsulfonic acidresins.

The phenolsulfonic acid resins are preferably present as salts. Thecondensation products of the present invention preferably have a degreeof condensation in the range from 1 to 20 and an average molecularweight of 500-10 000 g/mol. The phenolsulfonic acid resins arepreferably prepared similarly to the way indicated in EP-A 816 406.

Useful cationic polyelectrolytes include for example polymers from thegroup of the

-   (a) polymers comprising vinylimidazolium units,-   (b) polydiallyldimethylammonium halides,-   (c) polymers comprising vinylamine units,-   (d) polymers comprising ethyleneimine units,-   (e) polymers comprising dialkylaminoalkyl acrylate and/or    dialkylaminoalkyl methacrylate units, and-   (f) polymers comprising dialkylaminoalkylacrylamide and/or    dialkylaminoalkyl-methacrylamide units.

Such polymers are known and commercially available. The monomersunderlying the cationic polyelectrolytes of groups (a)-(f) can be usedfor polymerization in the form of the free base, but preferably in theform of their salts with mineral acids such as hydrochloric acid,sulfuric acid or phosphoric acid and also in quaternized form. Usefulquaternizing agents include for example dimethyl sulfate, diethylsulfate, methyl chloride, ethyl chloride, cetyl chloride or benzylchloride.

Examples of cationic polyelectrolytes are

-   (a) homopolymers of vinylimidazolium methosulfate and/or copolymers    of vinylimidazolium methosulfate and N-vinylpyrrolidone,-   (b) polydiallyldimethylammonium chlorides,-   (c) polyvinylamines and also partially hydrolyzed    polyvinylformamides,-   (d) polyethyleneimines-   (e) polydimethylaminoethyl acrylate, polydimethylaminoethyl    methacrylate, copolymers of acrylamide and dimethylaminoethyl    acrylate and copolymers of acrylamide and dimethylaminoethyl    methacrylate, for which the basic monomers can also be present in    the form of the salts with mineral acids or in quaternized form, and-   (f) polydimethylaminoethylacrylamide,    polydimethylaminoethylmethacrylamide and copolymers of acrylamide    and dimethylaminoethylacrylamide, for which the cationic monomers    can also be present in the form of the salts with mineral acids or    in quaternized form.

The average molar masses M_(w) of the cationic polyelectrolytes are atleast 500 g/mol. They are for example in the range from 500 g/mol to 10million g/mol, preferably in the range from 1000 to 500 000 g/mol andusually in the range from 1000 to 5000 g/mol.

Preference for use as cationic polymers is given to

-   (a) homopolymers of vinylimidazolium methosulfate and/or copolymers    of vinylimidazolium methosulfate and N-vinylpyrrolidone having an    average molar mass M_(w) of 500 to 10 000 g/mol in each case,-   (b) polydiallyldimethylammonium chlorides having an average molar    mass M_(w) of 1000 to 10 000 g/mol,-   (c) polyvinylamines and partially hydrolyzed polyvinylformamides    having an average molar mass M_(w) of 500 to 10 000 g/mol, and-   (d) polyethyleneimines having an average molar mass M_(w) of 500 to    10 000 g/mol.

The copolymers of vinylimidazolium methosulfate and N-vinylpyrrolidonewhich are mentioned under (a) comprise, for example, from 10% to 90% byweight of N-vinyl-pyrrolidone incorporated in the form of polymerizedunits. Instead of N-vinylpyrrolidone, it is possible to use, as acomonomer, at least one compound from the group consisting of theethylenically unsaturated C₃- to C₅-carboxylic acids, such as, inparticular, acrylic acid or methacrylic acid, or the esters of thesecarboxylic acids with monohydric alcohols comprising 1 to 18 carbonatoms, such as methyl acrylate, ethyl acrylate, isopropyl acrylate,n-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethylmethacrylate or n-butyl methacrylate.

A preferred polymer of group (b) is polydiallyldimethylammoniumchloride. Also suitable are copolymers of diallyldimethylammoniumchloride and dimethylaminoethyl acrylate, copolymers ofdiallyldimethylammonium chloride and dimethylaminoethyl methacrylate,copolymers of diallyldimethylammonium chloride and diethylaminoethylacrylate, copolymers of diallyldimethylammonium chloride anddimethylaminopropyl acrylate, copolymers of diallyldimethylammoniumchloride and dimethylaminoethylacrylamide and copolymers ofdiallyldimethylammonium chloride and dimethylaminopropyl-acrylamide. Thecopolymers of diallyldimethylammonium chloride comprise, for example,from 1 to 50, in general from 2 to 30, mol % of at least one of saidcomonomers incorporated in the form of polymerized units.

Polymers (c) comprising vinylamine units are obtainable bypolymerization of N-vinyl-formamide, if appropriate in the presence ofcomonomers, and hydrolysis of the polyvinylformamides with eliminationof formyl groups with formation of amino groups. The degree ofhydrolysis of the polymers may be, for example, from 1% to 100% and ispreferably in the range from 60% to 100%. In the realm of the presentapplication, partially hydrolyzed polyvinylformamides have a degree ofhydrolysis of ≧50% and preferably of ≧90%. The preparation of homo- andcopolymers of N-vinylformamide and the hydrolysis of these polymers withformation of polymers comprising vinylamine units are described indetail, for example, in U.S. Pat. No. 6,132,558, column 2, line 36 tocolumn 5, line 25. The statements made there are hereby incorporated byreference in the disclosure of the present invention. Polymerscomprising vinylamine units are sold, for example, as Catiofast® andPolymin® brands by BASF Aktiengesellschaft.

Polymers of group (d) which comprise ethyleneimine units, such aspolyethylene-imines, are likewise commercial products. They are sold,for example, under the name Polymin® by BASF Aktiengesellschaft, e.g.Polymin® SK. These cationic polymers are polymers of ethyleneimine whichare prepared by polymerization of ethyleneimine in an aqueous medium inthe presence of small amounts of acids or acid-forming compounds, suchas halogenated hydrocarbons, e.g. chloroform, carbon tetrachloride,tetrachloro-ethane or ethyl chloride, or are condensates ofepichlorohydrin and compounds comprising amino groups, such as mono- andpolyamines, e.g. dimethylamine, diethylamine, ethylenediamine,diethylenetriamine and triethylenetetramine, or ammonia. They have, forexample, molar masses M_(w), of from 500 to 1 million, preferably from1000 to 500 000 g/mol.

This group of cationic polymers also includes graft polymers ofethyleneimine on compounds which have a primary or secondary aminogroup, e.g. polyamidoamines of dicarboxylic acids and polyamines. Thepolyamidoamines grafted with ethyleneimine can, if appropriate, also bereacted with bifunctional crosslinking agents, for example withepichlorohydrin or bischlorohydrin ethers of polyalkylene glycols.

Suitable cationic polymers of group (e) are polymers comprisingdialkylaminoalkyl acrylate and/or dialkylaminoalkyl methacrylate units.These monomers can be used in the form of the free bases but arepreferably used in the form of the salts with mineral acids, such ashydrochloric acid, sulfuric acid or phosphoric acid, and in quaternizedform in the polymerization. Suitable quaternizing agents are, forexample, dimethyl sulfate, diethyl sulfate, methyl chloride, ethylchloride, cetyl chloride or benzyl chloride. Both homopolymers andcopolymers can be prepared from these monomers. Suitable comonomers are,for example, acrylamide, methacrylamide, N-vinylformamide,N-vinylpyrrolidone, methyl acrylate, ethyl acrylate, methyl methacrylateand mixtures of said monomers.

Cationic polymers of group (f) are polymers which comprisedimethylaminoethyl-acrylamide or dimethylaminoethylmethacrylamide unitsand which comprise the cationic monomers preferably in the form of thesalts with mineral acids or in quaternized form. These may behomopolymers and copolymers. Examples are homopolymers ofdimethylaminoethylacrylamide which is completely quaternized withdimethyl sulfate or with benzyl chloride, homopolymers ofdimethylaminoethyl-methacrylamide which is completely quaternized withdimethyl sulfate, methyl chloride, ethyl chloride or benzyl chloride,and copolymers of acrylamide and dimethylamino-ethylacrylamidequaternized with dimethyl sulfate.

In addition to those polycations which are composed solely of cationicmonomers, amphoteric polymers may also be used as cationic polymers,provided that they carry a cationic charge overall. The cationic excesscharge in the amphoteric polymers is, for example, at least 5 mol %,preferably at least 10 mol %, and is generally in the range from 15 to95 mol %. Examples of amphoteric polymers having a cationic excesscharge are

-   -   copolymers of acrylamide, dimethylaminoethyl acrylate and        acrylic acid which comprise at least 5 mol % more of        dimethylaminoethyl acrylate than acrylic acid incorporated in        the form of polymerized units,    -   copolymers of vinylimidazolium methosulfate, N-vinylpyrrolidone        and acrylic acid which comprise at least 5 mol % more of        vinylimidazolium methosulfate than acrylic acid incorporated in        the form of polymerized units,    -   hydrolyzed copolymers of N-vinylformamide and of an        ethylenically unsaturated C₃- to C₅-carboxylic acid, preferably        acrylic acid or methacrylic acid, having a content of vinylamine        units which is at least 5 mol % higher than units of        ethylenically unsaturated carboxylic acids,    -   copolymers of vinylimidazole, acrylamide and acrylic acid, the        pH being chosen so that at least 5 mol % more vinylimidazole is        cationically charged than acrylic acid is incorporated in the        form of polymerized units.

Useful polyelectrolytes for the purposes of the present inventionfurther include biopolymers, such as alginic acid, gum arabic, nucleicacids, pectins, proteins, and also chemically modified biopolymers, suchas ionic or ionizable polysaccharides, examples beingcarboxymethylcellulose, chitosan, chitosan sulfate, and ligninsulfonate.

Preference is given to selecting the polyelectrolyte from the groupcomprising polyacrylic acids, phenolsulfonic acid precondensates,polydiallyldimethylammonium chlorides, polyvinylamines, partiallyhydrolyzed polyvinylformamides and polyethyleneimine.

One embodiment prefers anionic polyelectrolytes, in particular ofpolyacrylic acids and phenolsulfonic acid resins.

One embodiment prefers cationic polyelectrolytes, in particular ofgroups (b), (c) and (d), i.e., polydiallyldimethylammonium chlorides,polyvinylamines and partially hydrolyzed polyvinylformamides andpolyethyleneimines. Particular preference is given to usingpolydiallyldimethylammonium chlorides as cationic polyelectrolytes.

Polyelectrolyte-modified microcapsules are obtained by contacting themicrocapsules or preferably a microcapsular dispersion with one or morepolyelectrolytes if appropriate in water or in aqueous medium.

Preference is given to polyelectrolyte-modified microcapsules having anaverage particle size of 1.5-2.5 μm and of which 90% of the particleshave the particle size ≦4 μm and also to the combination of thepreferred embodiments. They are obtained by contacting microcapsulescomprising a capsule core and a capsule wall constructed from

-   30% to 90% by weight of one or more C₁-C₂₄-alkyl esters of acrylic    and/or methacrylic acid, acrylic acid, methacrylic acid and/or    maleic acid, preferably of one or more C₁-C₂₄-alkyl esters of    acrylic and/or methacrylic acid (monomers I),-   10% to 70% by weight of a mixture of divinyl and polyvinyl monomers    (monomers II), the fraction of polyvinyl monomers being in the range    from 2% to 90% by weight based on the monomers II, and also-   0% to 30% by weight of miscellaneous monomers (monomer III),    all based on the total weight of the monomer, the microcapsules    having an average particle size of 1.5-2.5 μm and 90% of the    particles having a particle size ≦4 μm, with one or more    polyelectrolytes in water or an aqueous medium. Preferably, a    microcapsular dispersion is contacted with one or more    polyelectrolytes.

They are preferably obtained by

-   a) producing an oil-in-water emulsion comprising the monomers, the    lipophilic substance and polyvinyl alcohol and/or partially    hydrolyzed polyvinyl acetate, the average size of the oil droplets    being 1.5-2.5 μm, and-   b) free-radically polymerizing the monomers of the oil-in-water    emulsion obtained by a) and isolating the microcapsules if    appropriate-   c) contacting the microcapsules or microcapsular dispersion obtained    in b) with one or more polyelectrolytes if appropriate in water or    in an aqueous medium.

The polyelectrolyte is added to the starting microcapsular dispersionwithout a solvent or in solution, preferably as an aqueous solution. Theamount of polyelectrolyte is in the range from 0.1% to 5% by weight andpreferably in the range from 0.25% to 1.5% by weight, based on thestarting microcapsular quantity.

The microcapsules of the present invention can subsequently be isolatedby spray drying, if appropriate. The process step of free-radicalpolymerization b) produces a starting microcapsular dispersion as anintermediate product, which is contacted with the polyelectrolyte instep c). The particle size distribution of the polyelectrolyte-modifiedmicrocapsular dispersion is unchanged relative to the startingmicrocapsular dispersion. Preferably, the microcapsular dispersionobtained from process step b) is contacted with one or morepolyelectrolytes, i.e., without intervening isolation of themicrocapsules. Since an aqueous dispersion is present in this case, thedesired medium in which the microcapsules and the polyelectrolyte can bebrought into contact is already at disposal. Contacting or bringing intocontact is to be understood as meaning for example mixing with customarystirrers or mixers.

The microcapsules of the present invention can be processed directly asaqueous microcapsular dispersion or in the form of a powder. When usedin the textile sector, the microcapsules have good durability to drycleaning and also good evaporation rates. They also have good foggingvalues.

The microcapsular powder of the present invention has diverse uses. Itis very useful for modifying fibers and textile articles of manufacture,for example textile wovens and nonwovens (batts for example). Usefulapplication forms here include in particular microcapsular coatings,foams with microcapsules and microcapsule-modified textile fibers. Forcoatings, the microcapsules are applied to a textile article ofmanufacture together with a polymeric binder and if appropriate otherauxiliary materials, generally as a dispersion. Customary textilebinders are film-shaping polymers having a glass transition temperaturein the range from −45 to 45° C. preferably −30 to 12° C. The productionof such microcapsular coatings is described for example in WO 95/34609,expressly incorporated by reference. The modification of foams withmicrocapsules is effected in a similar manner as described in DE 981576Tand U.S. Pat. No. 5,955,188. The prefoamed substrate, preferably apolyurethane or polyether, is surface treated with a binder-containingmicrocapsular dispersion. The binder-microcapsule mixture issubsequently brought, by application of reduced pressure, into theopen-cell foam structure in which the binder cures and binds themicrocapsules to the substrate. A further processing possibility is tomodify the textile fibers themselves, as by spinning from a melt or anaqueous dispersion as described in US 2002/0054964 for example. Meltspinning processes are employed for nylon fibers, polyester fibers,polypropylene fibers and similar fibers, whereas the wet spinningprocess is utilized for the production of acrylic fibers in particular.

A further broad field of application is that of bindered buildingmaterials comprising mineral, silicatic or polymeric binders. Adistinction is made between shaped articles and coating compositions.They are notable for their hydrolytic stability to the aqueous and oftenalkaline aqueous materials.

The term mineral shaped article refers to a shaped article formed, aftershaping, from a mixture of a mineral binder, water, aggregates and also,if appropriate, auxiliaries by the hardening of the mineral binder/watermixture as a function of time, with or without the action of elevatedtemperature. Mineral binders are common knowledge. They comprise finelydivided inorganic substances such as lime, gypsum, clay, loam and/orcement, which are converted to their ready-to-use form by pasting withwater and in this form, when left to themselves, undergo consolidationas a function of time to a stonelike mass in air or even under water,with or without the action of elevated temperature.

The aggregates consist in general of granular or fibrous natural orsynthetic rock (gravel, sand, glass fibers or mineral fibers) or else,in special cases, of metals or organic aggregates or of mixturesthereof, having grain sizes or fiber lengths in each case adapted to theintended application in a conventional manner. In many cases, chromaticpigments are also used as aggregates for coloring purposes.

Useful auxiliaries include in particular those substances which hastenor delay hardening or which influence the elasticity or porosity of theconsolidated mineral shaped article. In particular, they are polymersknown for example from U.S. Pat. No. 4,340,510, GB patent 1 505 558,U.S. Pat. No. 3,196,122, U.S. Pat. No. 3,043,790, U.S. Pat. No.3,239,479, DE-A 43 17 035, DE-A 43 17 036, JP-A 91/131 533 and otherreferences.

The microcapsules of the present invention are suitable for modifyingmineral bindered building materials (mortarlike preparations) comprisinga mineral binder which consists of from 70% to 100% by weight cement and0% to 30% by weight gypsum. This holds in particular when cement is thesole mineral binder. The effect of the present invention is essentiallyindependent of the type of cement. Depending on the product at hand,therefore, it is possible to use blast furnace cement, oil shale cement,Portland cement, hydrophobicized Portland cement, quick-setting cement,high-expansion cement or high-alumina cement, the use of Portland cementproving to be particularly favorable. For further details reference maybe made to DE-A 196 23 413. Typically, the dry compositions of mineralbindered building materials comprise from 0.1% to 20% by weight ofmicrocapsules, based on the amount of mineral binder.

The microcapsules of the present invention are preferably incorporatedin mineral coating compositions such as render. A render of this kindfor the interior sector is typically composed of gypsum binder. Theweight ratio of gypsum/microcapsule is generally in the range from 95:5to 70:30. Higher microcapsular fractions are possible of course.

Coatings for the exterior sector such as exterior facings or moistenvironments may comprise cement (cementiceous renders), lime orwaterglass (mineral or silicate renders) or polymeric dispersions(synthetic-resin renders) as a binder together with fillers and, ifappropriate, pigments for coloration. The fraction of total solidsaccounted for by the microcapsules corresponds to the weight ratios forgypsum renders.

The microcapsules of the present invention are further useful inpolymeric shaped articles or polymeric coating compositions. By theseare meant thermoplastic and thermoset plastics materials whoseprocessing does not entail destruction of the microcapsules. Examplesare epoxy, urea, melamine, polyurethane and silicone resins and alsocoating materials—solventbornes, high solids, powder coatings orwaterbornes—and dispersion films. The microcapsular powder is alsosuitable for incorporation in polymeric foams and fibers. Examples offoams are polyurethane foam, polystyrene foam, latex foam and melamineresin foam.

The microcapsules of the present invention are further useful inlignocellulosic shaped articles such as chipboard.

Advantageous effects can further be achieved if the microcapsules of thepresent invention are processed in mineral shaped articles which aresubjected to foaming.

The microcapsules of the present invention are further useful formodifying gypsum plasterboard. Microcapsular powder is incorporated inan amount which is preferably in the range from 5% to 40% by weight andin particular in the range from 20% to 35% by weight based on the totalweight of the gypsum plasterboard (dry matter). The production of gypsumplasterboard comprising microencapsulated latent heat storage media iscommon knowledge and described in EP-A 1 421 243, expressly incorporatedherein by reference. Instead of cellulose-based card it is also possibleto use alternative, fibrous structures as both sided covers for the“gypsum plasterboard”. Alternative materials are polymeric fiberscomposed for example of polypropylene, polyester, polyamide,polyacrylates, polyacrylonitrile and the like. Glass fibers are suitableas well. The alternative materials can be employed as wovens and asnonwovens. Such building boards are known for example from U.S. Pat. No.4,810,569, U.S. Pat. No. 4,195,110 and U.S. Pat. No. 4,394,411.

The microcapsules of the present invention are further useful forproducing heat transfer fluid. Heat transfer fluid herein refers notonly to fluids for heat transport but also to fluids for cold transport,i.e., cooling fluids. The principle of the transfer of thermal energy isthe same in the two cases and only differs in the direction of transfer.

The examples which follow illustrate the invention. The percentages inthe examples are by weight unless stated otherwise.

The particle size of the microcapsular powder was determined using a3600E Malvern Particle Sizer in accordance with a standard method ofmeasurement which is documented in the literature. The D(0.1) value saysthat 10% of the particles have a particle size (by volume average) up tothis value. Correspondingly, D(0.5) means that 50% of the particles havea particle size (by volume average) of not more than this value. Thespan value is the quotient of the difference (D(0.9)−D(0.1)) and D(0.5).

Determination of Evaporation Rate

By way of pretreatment, 2 g of the microcapsular dispersion were driedin a metal dish at 105° C. for two hours to remove any residual water.Then, the weight (m_(o)) was determined. After one hour of heating at180° C. and cooling, the weight is redetermined (m₁). The weightdifference (m₀−m₁) based on m₀ and multiplied by 100 is the evaporationrate in %. The smaller the value, the better the tightness of themicrocapsules. It should be borne in mind that comparisons with regardto evaporation rate should always be carried out for comparable capsulesizes and stabilizer systems.

Production of Microcapsular Dispersion EXAMPLES 1A AND 1B CapsulesStabilized by Inorganic Pickering Systems EXAMPLE 1A Not InventiveAqueous Phase

-   630 g of water-   110 g of a 50% colloidal dispersion of SiO₂ in water at pH 9.2    (particle size about 80-100 nm)-   20.0 g of a 1% by weight aqueous solution of    methylhydroxyethylcellulose (Culminal® MHEC 15000 PFR)-   2.1 g of a 2.5% by weight aqueous sodium nitrite solution

Oily Phase

-   431 g of technical grade paraffin cut, C₁₆-C₁₈ (about 92% C₁₈)-   9 g of Sasol wax 6805 (high-melting paraffin)-   82.5 g of methyl methacrylate (MMA)-   27.5 g of butanediol diacrylate (BDA₂)-   0.76 g of ethylhexyl thioglycolate-   0.92 g of a 75% by weight solution of tert-butyl perpivalate in    aliphatic hydrocarbons

Addition 1

7.65 g of a 10% by weight aqueous solution of tert-butyl hydroperoxide

Feed Stream 1

28.34 g of a 1.1% by weight aqueous solution of ascorbic acid

-   a) The aqueous phase was introduced as initial charge and adjusted    to pH 2.5 with 20% by weight sulfuric acid. At 40° C., the oily    phase was added and the mixture was dispersed with a high-speed    dissolver at 3500 rpm for 40 minutes to obtain a stable emulsion.-   b) The emulsion, while being stirred with an anchor stirrer, was    heated to 67° C. over 60 minutes, heated to 85° C. in the course of    a further 60 minutes and maintained at 85° C. for one hour. Addition    1 was added and the resulting microcapsular dispersion was cooled    down to 20° C. with stirring in the course of 30 minutes, while feed    stream 1 was added over a period of 80 minutes.

This gave a microcapsular dispersion having a solids content of 43.8% byweight and an average particle size of D[4,3]=8.34 μm, span=0.98. Theevaporation rate was 70.6%, and the fogging value was 1.3 mg/g.

EXAMPLE 1B

Example 1a was repeated except that 50% by weight of the butanedioldiacrylate was replaced by pentaerythritol tetraacrylate (PETIA).

This gave a microcapsular dispersion having a solids content of 39.3% byweight and an average particle size of D[4,3]=5.82 μm, span=1.01. Theevaporation rate was 64.6%.

EXAMPLES 2A-2E Aqueous Phase

-   380 g of water-   190 g of a 5% by weight aqueous dispersion of    methylhydroxypropylcellulose (Culminal® MHPC 100)-   47.5 g of a 10% by weight aqueous polyvinyl alcohol solution (Mowiol    15-79)-   2.1 g of a 2.5% by weight aqueous sodium nitrite solution

Oily Phase

-   431 g of technical grade octadecane (95% by weight purity)-   9 g of Sasol wax 6805 (high-melting paraffin)-   19.6 g of methyl methacrylate-   19.6 g of crosslinker mixture, see table 1-   9.8 g of methacrylic acid-   0.7 g of a 75% by weight solution of tert-butyl perpivalate in    aliphatic hydrocarbons

Addition 1

5.38 g of a 10% by weight aqueous solution of tert-butyl hydroperoxide

Feed Stream 1

28.3 g of a 1.1% by weight aqueous solution of ascorbic acid

-   a) At 40° C., the above aqueous phase was introduced as initial    charge and after addition of the oily phase the mixture was    dispersed with a high-speed dissolver at 3500 rpm. A stable emulsion    was obtained after 40 minutes of dispersion.-   b) The emulsion, while being stirred with an anchor stirrer, was    heated to 70° C. over 60 minutes, heated to 85° C. in the course of    a further 60 minutes and maintained at 85° C. for one hour. Addition    1 was added and the resulting microcapsular dispersion was cooled    down to 20° C. with stirring in the course of 30 minutes, while feed    stream 1 was added.

The characteristics of the resulting microcapsular dispersions arerevealed in table 1. The microcapsules had an average particle size ofD[4,3]=3-5 μm.

TABLE 1 Microcapsules from different crosslinker mixtures Crosslinkermixture Solids Evaporation BDA₂ PETIA D[4, 3] content rate Example [wt%] [wt %] [μm] Span [%] [%] 2a 100 0 4.58 1.01 44.0 11.3 2b 95 5 3.480.84 42.6 6.7 2c 87.5 12.5 3.58 1.12 43.1 3.9 2d 75 25 3.76 0.91 43.43.9 2e 0 100 3.66 0.94 43.2 30.4 BDA₂: butanediol diacrylate PETIA:pentaerythritol tetraacrylate

Examples 2a and 2e are not inventive.

EXAMPLES 3A-3H Aqueous Phase

425 g of water412 g of a 10% by weight aqueous polyvinyl alcohol solution (Mowiol40-88)2.1 g of a 2.5% by weight aqueous sodium nitrite solution

Oily Phase

-   431 g of a technical grade paraffin cut, C₁₆-C₁₈ (about 92% C₁₈)-   9 g of Sasolwax 6805 (high-melting paraffin)-   77.6 g of monomer mixture, as per table 2-   0.76 g of ethylhexyl thioglycolate-   0.7 g of a 75% by weight solution of tert-butyl perpivalate in    aliphatic hydrocarbons

Addition 1

5.38 g of a 10% by weight aqueous tert-butyl hydroperoxide solution,

Feed Stream 1

28.3 g of a 1.1% by weight aqueous ascorbic acid solution

Addition 2

1.00 g of a 25% aqueous sodium hydroxide solution1.43 g of water

-   a) At 70° C., the above aqueous phase was introduced as initial    charge and after addition of the oily phase the mixture was    dispersed with a high-speed dissolver at 6000 rpm. A stable emulsion    of average particle size D[4,3]=2.3 μm diameter was obtained after    40 minutes of dispersion.-   b) The emulsion, while being stirred with an anchor stirrer, was    heated to 70° C. over 60 minutes, heated to 85° C. in the course of    a further 60 minutes and maintained at 85° C. for one hour. Addition    1 was added and the resulting microcapsular dispersion was cooled    down to 20° C. with stirring in the course of 30 minutes, while feed    stream 1 was added. Addition 2 was added to adjust the pH to 7.

The characteristics of the microcapsular dispersions obtained aredescribed in table 2.

TABLE 2 Evaporation rate from different monomer mixtures (monomer datain % by weight) Example 3a (comparative) 3b 3c 3d 3e 3f 3g 3h Monomermixture 65% MMA 65% MMA 65% MMA 65% MMA 65% MMA 45% MMA 25% MMA 5% MMAMonomers Ia 10% MAS 10% MAS 10% MAS 10% MAS 10% MAS 30% MAS 50% MAS 70%MAS Monomers 1b 25% BDA₂ 20% BDA₂ 15% BDA₂ 10% BDA₂ 5% BDA₂ 15% BDA₂ 15%BDA₂ 15% BDA₂ Monomers II 0% PETIA 5% PETIA 10% PETIA 15% PETIA 20%PETIA 10% PETIA 10% PETIA 10% PETIA Ratio BDA₂/PETIA 100/0 80/20 60/4040/60 20/80 60/40 60/40 60/40 D[4, 3] [μm] 2.06 2.04 1.94 1.91 1.87 1.81.94 2.3 Span 0.35 0.35 0.34 0.35 0.30 0.25 0.35 0.3 Solids content [%]40.6 40.0 40.1 40.1 40.8 40.1 40.5 40.7 Evaporation rate [%] 22.7 7.06.3 8.3 9.7 2.4 7.2 2.8 Evaporation rate¹⁾ [%] 3.6 1.8 2.2 2.0 1.9 1.24.4 2.1 MMA: methyl methacrylate BDA₂: butanediol diacrylate PETIA:pentaerythritol tetraacrylate MAS: methacrylic acid ¹⁾A sample of eachof the microcapsular dispersions of Examples 3a-3h was admixed with a50% by weight aqueous solution of a phenolsulfonic acid-formaldehyderesin (M_(w) = 7000 g/mol), amount: 1% by weight ofresin_(solid)/microcapsules_(solid)) and subsequently the evaporationrate was determined.

1. A microcapsule comprising a capsule core and a capsule wall, thecapsule wall being constructed from 30% to 90% by weight of one or moreC₁-C₂₄-alkyl esters of acrylic and/or methacrylic acid, acrylic acid,methacrylic acid and/or maleic acid (monomers I), 10% to 70% by weightof a mixture of divinyl and polyvinyl monomers (monomers II), thefraction of polyvinyl monomers being in the range from 2% to 90% byweight based on the monomers II, and also 0% to 30% by weight of one ormore miscellaneous monomer (monomer III), all based on the total weightof the monomers.
 2. Microcapsules comprising a capsule core and acapsule wall, the capsule wall being constructed from 30% to 90% byweight of one or more C₁-C₂₄-alkyl esters of acrylic and/or methacrylicacid, acrylic acid, methacrylic acid and/or maleic acid (monomers I),10% to 70% by weight of a mixture of divinyl and polyvinyl monomers(monomers II), the fraction of polyvinyl monomers being in the rangefrom 2% to 90% by weight based on the monomers II, and also 0% to 30% byweight of one or more miscellaneous monomer (monomer III), all based onthe total weight of the monomers, wherein the microcapsules have anaverage particle size of 1.5-2.5 μm and 90% of the particles have aparticle size ≦4 μm.
 3. The microcapsules according to claim 2 whereinthe fraction of the polyvinyl monomers is in the range from 5% to 80% byweight based on the sum total of divinyl and polyvinyl monomers.
 4. Themicrocapsule according to claim 1 wherein the polyvinyl monomer isselected from the group comprising trimethylolpropane triacrylate,trimethylolpropane trimethacrylate, pentaerythritol triallyl ether,pentaerythritol tetraallyl ether, pentaerythritol triacrylate andpentaerythritol tetraacrylate.
 5. The microcapsule according to claim 1wherein the capsule core is a lipophilic substance having a solid/liquidphase transition in the temperature range from −20 to 120° C.
 6. Themicrocapsule according to claim 1 wherein additionally polyelectrolyteshaving an average molecular weight in the range from 500 g/mol to 10million g/mol are disposed on the outer surface of the capsule wall. 7.The microcapsule according to claim 6 wherein the polyelectrolytequantity is in the range from 0.1% to 10% by weight based on the totalweight of the polyelectrolyte-bearing microcapsules.
 8. Themicrocapsules according to claim 2 in the form of an aqueous dispersion.9. A process for producing microcapsules according to claim 2, whereineach microcapsule comprises a capsule core and a capsule wall, thecapsule wall being constructed from 30% to 90% by weight of one or moreC₁-C₂₄-alkyl esters of acrylic and/or methacrylic acid, acrylic acid,methacrylic acid and/or maleic acid (monomers I), 10% to 70% by weightof a mixture of divinyl and polyvinyl monomers (monomers II), thefraction of polyvinyl monomers being in the range from 2% to 90% byweight based on the monomers II, and also 0% to 30% by weight ofmiscellaneous monomers (monomer III), all based on the total weight ofthe monomer, said process comprising heating an oil-in-water emulsion inwhich the monomers, a free-radical initiator and the lipophilicsubstance are present as the disperse phase.
 10. The process forproducing microcapsules according to claim 9 by a) producing anoil-in-water emulsion comprising the monomers, the lipophilic substanceand polyvinyl alcohol and/or partially hydrolyzed polyvinyl acetate, theaverage size of the oil droplets being 1.5-2.5 μm, and b) free-radicallypolymerizing the monomers of the oil-in-water emulsion obtained by a).11. The process for producing microcapsules according to claim 9 bycontacting the microcapsular dispersion with one or morepolyelectrolytes.
 12. A method of using the microcapsules according toclaim 2 for incorporation in textiles.
 13. A method of using themicrocapsules according to claim 2 in bindered building materials.
 14. Amethod of using the microcapsular dispersion according to claim 2 inheat transfer fluids.